This application relates to German patent application no. 199 12 461.2 filed Mar. 19, 1999, the disclosure of which is incorporated herein by reference in its entirety.
The present invention relates to a device for flow rate limitation at low differential pressures, particularly for limiting the volumetric inhalation flow during inhalation of therapeutic aerosols.
In the field of aerosol therapy it is important for the envisaged administration of the medicament that firstly a defined volumetric inhalation flow will not be exceeded and secondly that a pressure drop will occur at volumetric flows below the maximum volumetric flow, which is as low as possible. The flow rate limiting devices so far know fail to satisfy these conditions because in the majority of cases they operate only at pressures by far higher than 100 millibar above atmospheric pressure.
The present invention is intended to make a novel device available which is suitable for achieving a volumetric flow limitation as envisaged for the intended purpose during the inhalation of therapeutic aerosols.
This problem is solved In accordance with the present invention by the features defined in Patent claim 1. Preferred features which constitute expedient improvements of the invention may be taken from the dependent Claims.
Based on the inventive concept it is now possible in an expedient manner to make a device available for limiting the inhaled volume during the inhalation of therapeutic aerosols, wherein an automatic mechanical volumetric flow control commences at pressures as low as 5 millibar. On account of the selection of the flexibility or elasticity, respectively of the material for the wall sections of the flow passage, which bend inwards for narrowing the cross-section of the passage as a function of the subatmospheric pressure prevailing in the flow passage, it is now expediently possible at an extraordinarily low engineering expenditure to achieve an adaptation to various volumetric maximum flow rates. When moreover the material used for the production of the device consists of a biologically tolerable synthetic material, particularly when the flow passage is made of silicone, an excellent suitability for the clinical application is achieved.
In correspondence with a preferred embodiment the flow passage is configured to have a flat elongate cross-section which is formed to have opposing large-area walls. This configuration enhances the inward bending of the walls for a reduction of the cross-section of the passage.
In correspondence with a preferred further embodiment of the invention the opposing walls are open on their outside, at least in the central area between the aspiration and inhalation orifices, to the environment, with each wall having preferably one chamber section on its outside, which is open via a bore to the environment, at least in the central area between the aspiration and inhalation orifices. With these structural provisions the required pressure equalization is expediently ensured when the walls are contracted.
Moreover structurally simple provisions are made for a stratified structure of the flow passage, which comprises preferably a closed wall, a frame-shaped partition of the same size, and a wall of equal size with an aspiration and inhalation orifice, with the opposite walls being fastened on the sides of their edges in the housing.
Any flexible and biologically tolerable material is suitable for configuring the flow passage, which material is flexible and can also be returned into its original shape after bending. It is preferred that at least the large-area passage walls, preferably also the partition, consist of silicone mats whilst the housing is made of a preferably biologically tolerable synthetic material.
In correspondence with a special embodiment of the invention the material layers of the flow passage are fastened for exchange between two housing sections. With such a structure it is possible in a simple manner to use one device for different flow rate limiting parameters with a correspondingly associated flow passage. Each of the large-area passage walls has preferably the same thickness.
According to an alternative further embodiment of the invention expedient provisions are made for an integral structure of the flow passage, preferably in the form of a silicone element, instead of a stratified structure.
In correspondence with another embodiment of the invention provisions are made for a flow rate limitation independent of the environmental pressure, wherein each wall comprises on its outside a chamber section with a bore at least in the central area between the aspiration and inhalation orifices, which bores communicate with the aspiration orifice through a passage or a hose, respectively. With these provisions the differential pressure between the aspiration and inhalation orifices is measured, which is decisive for control, and flow rate limitation could also be operated in a closed system.
According to a further embodiment of the invention the flow passage may have an annular cross-section, instead of a flat elongate cross-section, with the flow passage being preferably symmetrically disposed in a cylindrical housing at a spacing from the inside cylinder wall, between radial disks. These retainer disks are preferably provided with aspiration and inhalation orifices having the shape of ring segments, with the retainer disk with the aspiration orifices having pressure equalizing bores for the cylindrical inside area and the annular zone surrounding the flow passage. This annular flow passage, too, is preferably formed of silicone.
In accordance with another alternative embodiment of the invention provisions are made for the formation of the flow region between a central inhalation orifice and aspiration orifices radially surrounding them which region presents star-shaped or radial webs extending from a common bottom surface to the flexible wall and forming flow passages which can be restricted. With these provisions the device can be designed with an extraordinarily compact structure, is easy to manufacture and to replace.
The webs forming flow passages may have different lengths so that in the region of the longer webs a wider flow passage will be formed which then splits into several flow passages at intermediately arranged shorter webs. The cross-section of the webs may be constant in a radial direction. The webs are expediently flaring outwardly over their width, with one aspiration orifice being preferably provided between two adjacent webs.
In an advantageous disposable embodiment, which is suitable for mass production, the device can be expediently realized with a disk-shaped basic body wherein the webs are integrally formed between flat recesses and inhalation orifices are formed on the edge side in the recesses, as well as with a thin flexible mat with a central aspiration orifice, which rests on the webs and is fastened in the edge region of the basic body. The mat may be adhesively fastened or welded, respectively, or clamped by means of an annular assembly element in the edge region of the basic body.
The thin flexible mat consists preferably of silicone, silicone rubber, Viton, latex, natural rubber or any other elastomer.